American Journal of Polymer Science 2012, 2(4): 73-78 DOI: 10.5923/j.ajps.20120204.05

Modification and Characterization of Polyacrylic Acid for Metal Ion Recovery

Magdy Y. Abdelaal1,2,*, Mohammad S.I. Makki1, Tariq R.A. Sobahi1

1Chemistry Department, Faculty of Science, King Abdulaziz University, PO Box 80203, Jeddah 21589, Saudi Arabia 2Chemistry Department, Faculty of Science, Mansoura University, 35516, Mansoura, Egypt [email protected], [email protected]

Abstract Polyacrylic acid was converted into modified polymers with the targeted functional groups through the reaction with different organic compounds such as some aromatic amines and acids. The obtained modified polymeric products have been characterized through FT-IR spectroscopic and thermal analyses. Modified acrylic polymers were tested for their ability to be used for heavy metal ion recovery from their aqueous solutions. They also were tested as polymeric antioxidants for PVC as a standard polymer by using the discoloration extent of PVC as a function of thermal degradation of PVC due to the thermal treatment. The obtained results were discussed and justified. Keywords Modification, Polyacrylic Acid, Metal Ion Recovery, Thermal Stability, Aromatic Amines

1. Introduction chemistry and technology of biopolymer for medical applications[9]. The two problems are creation of synthetic Polyacrylic acid (PAA) belongs to the class of commercial polymeric materials for short-time or prolonged contact with polymers produced on a large scale and widely used in blood and other tissues in the living organism and various industries, agriculture, and medicine[1]. PAA, its development of the synthesis methods, establishing the salts and PAA-based polymeric materials are used as mechanisms of physiological action of the macromolecules emulsifiers and thickening agents for aqueous solutions and of pharmaceutical preparations[10]. dispersions of both natural and synthetic latexes, smoothing Microwave initiated grafting of polyacrylic acid onto agents for synthetic fibers, sorbents and ion exchangers, carboxymethylcellulose (CMC) to synthesize CMC-g-PAA aqueous quenching media, flocculants, plastics, etc.[2-5]. which has showed higher flocculation efficiency than CMC Copolymers of acrylamide and divinylbenzene are used as itself reflecting the role of polyacrylic acid in such ion exchange resins as well as copolymers of acrylic acids application. The high flocculation efficiency of polyacrylic with acrylamide and polyvinyl alcohol are known for their acid grafted CMC makes it a good candidate as flocculants activity toward metal ion uptake to be applied in the metal for river water clarification[11]. ion preconcentration or removal[6]. Polymers and Synthesis of PAA and its properties have been extensively copolymers of acrylic acid are known as efficient flocculants studied and repeatedly reviewed. It will be only mentioned used, in particular, for increasing the strength of special briefly some points of importance. PAA is obtained by paper grades[7]. polymerization of acrylic acid (AA) in the presence of Hydrophilic properties of PAA explain its wider use in photo-initiators or under the action γ-radiation[12]. In the agriculture for presuming treatment of seeds, etc. In recent solid state, AA converts into polymer on exposure to UV years, there has been a growing interest in PAA as a basis for radiation. Hydrogen peroxide, alkali metal or ammonium obtaining various physiologically active polymeric persulfates, and cumene hudrogen peroxide initiate the substances capable of separating from the carrier molecule at polymerization of AA in aqueous solution. Only non-ionized definite site of the living organism and producing a targeted AA molecules enter into the polymerization reaction and the physiological action[8]. minimum reaction rate is observed. Both PAA and the related compounds are more widely Aqueous media are preferred for the polymerization of used as polymeric carriers for proteins, enzymes, drugs and AA whose concentration should not exceed 25% due to the other biologically active substances. In the latter case, PAA exothermic nature of the reaction which is otherwise difficult can be used for solving two mutually related problems of the to control. Polymerization of AA in non-aqueous solvents is initiated by organic peroxides, AIBN and some redox and * Corresponding author: [email protected] (Magdy Y. Abdelaal) other systems. Published online at http://journal.sapub.org/ajps The most active polymers on the basis of esters, Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved anhydrides, amides, and related PAA derivatives composed

Magdy Y. Abdelaal et al.: Modification and Characterization of Polyacrylic Acid for Metal Ion Recovery 74

of the –CH2-CH(C(=O)X)- units, where X is OR, OCOR, 2.2. Synthesis of Polyacrylic Acid NH2, NR2, etc., can be synthesized using three pathways. A solution of 0.2 mole of dibenzoylperoxide in THF was First is grafting of the reactive physiologically active added to 2 mole of acrylic acid solution in THF while stirring. monomers onto PAA matrix with the formation of valence The mixture was purged with nitrogen for 30 min at 70°C bonds. An example is the synthesis of some sulfanilamide and was continued for 30 min further at the same conditions preparations, hormones, and some other biologically active before cooling to the room temperature. Polyacrylic acid was compounds with reactive OH or NH2 groups[13]. The second precipitated by pouring into 400 ml of anhydrous diethyl one is the condensation of polyacrylyl chloride, polyacryla ether. The obtained product was filtered off and washed mide, polyalkylacrylate, or polyacrylic acid salt with successively with diethyl ether and methanol then dried physiologically active substance containing the correspondi overnight under vacuum at 40 °C. ng functional groups. The last one is the homo-polymerizati on of physiologically active acrylic acid substituent of the 2.3. Synthesis of Polyacryly Chloride formula CH =CH(C(=O)Y)- where Y is a pharmacophore 2 About 1.4 mole of thionyl chloride was added dropwisely group bound through oxygen or nitrogen atom. to 1 mole of polyacrylic acid in a round bottomed flask. The The first investigations in the synthesis of PAA reaction mixture was stirred for 1 h at 60°C and left to cool to derivatives containing reactive functional groups were the room temperature. The unreacted thionyl chloride was reported by Kern and Schulz[12,14]. By interaction of collected by filtration. The obtained product was washed polymethacrylate with hydrazine they obtained a with methylene chloride and dried overnight in vacuum at polyacryloylhydrazide which was converted by Curtius 40 °C. reaction into polyacryloylazide. This was followed by condensation with various carbonyl compounds yielding 2.4. Synthesis of Poly-2-acryloxybenzoic Acid polyacryloylhydrazones. A reaction of polymethylacrylate with hydroxylamine led to polyacryloylhydroxamic acid. A solution of 0.25 mole salicylic acid and 0.75 mole of Interaction of the latter acid with the salts of various metal triethylamine in 300 ml acetonitrite was added dropwise to ions led to a series of the corresponding metal containing 0.3 mole of polyacrylyl chloride pre-soaked in 100 ml derivatives. There are many trials to prepare modified acetonitrite for 6 h. After complete addition, the reaction polyacrylic acids through the synthesis of modified mixture was stirred further for 6 h at 25°C. The reaction monomers followed by their polymerization[15]. Although mixture was filtered off and washed with methanol, 1M HCl, modified polymers with higher purity would be obtained, the distilled water to remove the formed triethylamine chemical modification of the monomers is not simple and hydrochloride and finally with diethyl ether. The obtained need many precautions beside it is not suitable for the polyacryloxybenzoic acid was dried overnight under vacuum recycling of polyacrylic acid wastes. The current work is at 40 °C. aiming to preparation of different polyacrylic acid derivativ 2.5. Synthesis of Poly-N-acroylaniline es through simple methodologies followed by characterizati on and utilization of them as polymeric anti-oxidant and as a A cold solution of 0.07 mole of aniline in 100 methylene tool for recovery of heavy metals from their aqueous chloride was added portion-wise with stirring to 0.03 mole of solutions. polyacrylyl chloride soaked in 50 ml methylene chloride. After the complete addition stirring was continued for 30 2. Experimental Part min further and the product was filtered off. The excess of aniline was removed by washing the precipitate with 2.1. Materials and Techniques methylene chloride, acetone and methanol respectively and the obtained product was dried overnight under vacuum at 40 All chemicals were obtained from Aldrich and used as °C. In the same way, poly-N-acrylyl-8-aminoquinolione and received without further purification unless otherwise poly-N-acrylylnaphtylamine were prepared. mentioned. PVC (M.Wt.=100.000) was also obtained from Aldrich. 2.6. Synthesis of Poly-4-acryloxybenzalthiobarbituric FT-IR Spectroscopic analysis was carried out using a Acid Perkin-Elmer 1430 spectrophotometer in the range of 4000-400 cm-1. UV spectra were recorded on a double beam 0.2 mole of polyacrylyl chloride was dissolved in THF and spectrophotometer to measure the extent of discoloration of added drop-wise to a cold solution of 0.2 mole of the degraded PVC samples as a function of degradation time. 4-hydroxybenzalthiobarbituric acid and 20ml of triethylami ICP/AES in the department was used to determine the ne in 100 ml THF and stirred further for 24 h at room concentration of the heavy metal ions under investigation. temperature. The reaction mixture was poured portion-wise Differential thermal analysis (DTA) was carried out with a into dilute solution of HCl. The formed precipitate was Shimadzu thermo-analyzer (D-50), Japan. Samples were washed thoroughly with subsequent amounts of dilute HCl heated at 10 °C/min in a stream of dry nitrogen using sintered solution, methanol, acetone and diethyl ether. The product alumina (α-Al2O3) as thermally inert reference material. was then finally dried overnight under vacuum at 40 °C.

75 American Journal of Polymer Science 2012, 2(4): 73-78

2.7. Effect of Modified Polyacrylic Acid on Thermal Stability of PVC A solution of 10 g PVC was dissolved in 150 ml THF was mixed with 0.2 g of modified polyacrylic acid dissolved in THF with stirring followed by sonication of the mixture to remove all the trapped gases during mixing. After that, the mixture was casted on a polypropylene sheet mounted on a horizontal glass plate. After evaporation of the solvents at room temperature, the obtained film was dried overnight under vacuum at room temperature. Modified polyacrylic acids used were polyacrylyloxybenzoic acid and polyacrylyloxybenzalthiobarbituric acid. The obtained film was then cut into strips and thermally treated at 100 °C for Scheme 1. Chemical modification of polyacrylic acid different intervals. The discoloration extent of PVC blends attributed to dehydrohalogenation of PVC[16] was used as a function of thermal degradation of PVC and is related to the absorbance at λ =400nm for the blended films in comparison with a blank sample of PVC under comparable conditions. The absorbance was plotted against time of thermal treatment of PVC blends and calculated as an average of 3 replicates. Data of the investigation is summarized in Table 1. Figure 1. IR curve of poly-2-acryloxybenzoic acid Table 1. Effect of modified polyacrylic acid on the degradation of PVC TGA of poly-2-acrylyloxybenzoic acid in Figure 2 Time, min PVC PVC+PBA PTBA showed that the weight loss started at about 95 °C and 0 0 0 0 reached about 62% weight loss at 250 °C. About further 14% at 410 °C was also observed which indicates that 12 0.48 0.21 0.15 poly-2-acrylyloxybenzoic acid can be considered thermally 24 1.22 1.09 0.19 stable up to 250 °C. The weight loss in this case occurs mainly due to decarboxylation of polymer while the main 72 1.94 1.72 0.28 chain C-C fission started at 420 °C. 2.8. Metal Ion Recovery of Poly-2-acrylyloxybenzoic Acid 0.1 g portions of polyacrylyloxybenzoic acid were added separately to 100 ml solution of the studied heavy metal ions in 100 mg/l concentration after adjusting its pH at ~4.5. These solutions were shaken for 1 h. The polymer was filtered off and washed with double distilled water. The sorbed metal ions were eluted with 5 ml of 2M HCl and the metal ion uptake of the polymer (in mg/g) was calculated after determination of the eluted metal ions by ICP/AES technique. Figure 2. TGA of poly-2-acryloxybenzoic acid 3. Results and Discussion 3.3. Characterization of Poly-N-acrylylamines Chemical modification of polyacrylyl chloride with 3.1. Characterization of Poly-2-acrylyloxybenzoic Acid different amines such as aniline, α-naphthylamine and Chemical modification of polyacrylic acid with benzoic 8-aminoquinoline was carried out according Scheme 1. acid was performed according to Scheme 1. FT-IR spectrum of poly-N-acrylylaniline in Figure 3a shows FT-IR spectroscopic analysis in Figure 1 showed absorption band for COCl at 1660 cm-1 is absent, while the characteristic absorptions related to polyacrylic acid in absorption bands of N-H stretching and amidic C=O groups addition to the absorption corresponding to the aromatic appear at 3270 cm-1 and at 1610 cm-1, respectively indicating moiety at 1615 cm-1 and 1455 cm-1 beside the absorption of the successful modification of polyacrylyl chloride with free carboxylic and ester C=O groups at 1690 cm-1 and at aniline into polumer-supported amines. The same findings 1740 cm-1, respectively and OH stretching at 3030 cm-1. hold true for poly-N-acrylyl-α-naphthylamine. There are

Magdy Y. Abdelaal et al.: Modification and Characterization of Polyacrylic Acid for Metal Ion Recovery 76

also absorption bands at 1626 cm-1 related to C=C (olefinic) and at 1570 cm-1 related to C=N (aromatic) for poly-N-acrylyl-8-aminoquinoline shown in Figure 3b.

Figure 5. IR curve of poly-4-acryloxybenzalthiobabituric acids TGA analysis of poly-4-acrylyloxybenzalthiobarbituric acid shown in Figure 6 indicates that this polymer starts to degrade at relatively high temperature of about 235 °C. Such Figure 3. IR spectroscopic analysis of (a) poly-N-acrylylaniline and (b) weight loss attains about 52% of the original weight of the poly-N-acryloyl-8-aminoqionoline polymer sample.

TGA of poly-N-acrylylaniline showed that the polymer is thermally stable up to 235 °C with weight loss of about 48% of the initial weight in addition to another weight loss of about 9.6% at about 530 °C. This indicates that stability of the polymer against thermal effects is not very high and this may attributed to the ease of oxidation of the amino group followed by separation of aniline moiety from the polymer matrix. Figure 4 shows TGA of polyacrylic acid as a blank.

Figure 6. TGA of poly-4-acrylyloxybenzalthiobabituric acids The first stage of the weight loss seems to be due to the rupture of C-O bond leading to the liberation of thiobarbituric acid moiety. Raising the temperature leads to slight loss in weight attaining about 13.0% starting at 422 °C which may be attributed to C-C bond fission. This can be concluding that the behavior of poly-4-acrylyloxybenzalthio Figure 4. TGA polyacrylic acid barbituric acid is a typical behavior of normal polyolefins at higher temperatures. TGA for poly-N-acrylyl-α-naphthylamine showed almost 3.5. Stabilizing Effect of Modified Polyacrylic Acid on similar behaviour with weight loss of about 52% at 265 °C. PVC This reflects the relatively higher stability of polyacrylyl-α- naphthylamine against thermal effects than that for Poly-4-acrylyloxybenzalthiobarbituric acid and polyacryl polyacrylylaniline. However, poly-N-acrylylaniline and yloxybenzoic acid and were used as thermal stabilizers poly-N-acrylyl-α-naphthylamine showed higher thermal against autocatalytic dehydrochlorination reaction of PVC in stability relative to that of polyacrylyloxybenzoic acid which presence of modified acrylic polymers. This reaction causes suffers weight loss of about 62% until 250 °C that may be degradation of PVC which leads to a severe discoloration attributed to the ease of decarboxylation. and lack of mechanical properties of PVC[16]. Thiobarbituric acid-supported polymer possesses a variety of 3.4. Characterization of functional groups able to interfere with the degradation Poly-4-acrylyloxybenzalthiobarbituric Acid process and also to absorb HCl produced by degradation of PVC. This results in reduction or delay of the harmful effect Polyacrylyl chloride was reacted with4-hydroxybenzal-th of acidic degradation products[17]. iobarbituric acid to form polyacrylyloxybenzalthiobarbituric This can be proved by the stabilizing efficiency of acid shown in Scheme 1. FT-IR spectroscopic analysis in modified polyacrylic acids on the treated PVC reflected by Figure 5 showed absorption bands at 1170 cm-1 related to reducing the extent of discoloration of induced by thermal C=S bonds and at 1680 cm-1 and 1726 cm-1 related to C=O treatment of PVC in comparison with blank PVC. This can (ketone) and C=O (ester) groups, respectively. be attributed to the dehydrohalogenation of PVC under

77 American Journal of Polymer Science 2012, 2(4): 73-78

thermal treatment conditions[16,18,19]. Figure 7 shows a stability up to 235 °C while it was up to 265 °C for lower extent of discoloration of the treated PVC samples poly-N-acrylyl-α-naphthylamine. Beside thermal stability up relative to blank sample. These results confirm a mechanism to 235 °C, polyacrylyloxybenzalthiobarbituric acid showed involving an interaction of the thiobarbituric acid moiety also ability to be used as thermal stabilizer for PVC. (OBT) from the polymer with the chlorine atoms emitted Polyacrylyloxybenzoic acid showed different abilities to from the polymer and thus blocks the odd electron sites on recover different metal ions from their aqueous solutions PVC chains. which can be applied in many application directions such as This action suppresses the possibility for conjugation metal ion recovery from their aqueous solutions. rather than with HCl evolved. Presence of thiobarbituric acid with a spacer group of oxybenzal moiety helps for higher mobility of such side chains to catch emitted HCl relative to ACKNOWLEDGEMENTS the directly attached thiobarbituric acid moiety to polymeric backbone. This project was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, under grant no. 418/130/431. The authors, therefore, acknowledge

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